Self-adjusting load balancing pneumatic hoist

ABSTRACT

The present invention is directed to a pneumatic hoist incorporating a load balancing system whereby a load supported by the hoist may be vertically repositioned by applying a relatively small force against the load in the direction of desired movement. The load balancing system utilizes a pressure regulator which is capable of continuously maintaining the pressure in the hoist to equal a reference pressure automatically established as required to balance the load and sealed in a pilot chamber of the regulator to provide for the vertical displacement of the load in response to a relatively small force applied in the direction of the desired movement.

United States Patent Cobb [451 July 15,1975

[ SELF-ADJUSTING LOAD BALANCING PNEUMATIC I'IOIST William G. Cobb, OakRidge, Tenn.

Filed: Apr. 5, 1974 Appl. No.: 458,365

Inventor:

Assignee:

References Cited UNITED STATES PATENTS 8/1959 Bottje et al. 91/3902/1969 Powell 91/390 3,621,756 ll/l97l Ulbing ..9l/39O PrimaryExaminer-Paul E. Maslousky Attorney, Agent, or FirmDean E. Carlson;David S. Zachry; Earl L. Larcher [57] ABSTRACT The present invention isdirected to a pneumatic hoist incorporating a load balancing systemwhereby a load supported by the hoist may be vertically repositioned byapplying a relatively small force against the load in the direction ofdesired movement. The load balancing system utilizes a pressureregulator which is capable of continuously maintaining the pressure inthe hoist to equal a reference pressure automatically established asrequired to balance the load and sealed in a pilot chamber of theregulator to provide for the vertical displacement of the load inresponse to a relatively small force applied in the direction of thedesired movement.

5 Claims, 1 Drawing Figure COMPRESSED AIR SUPPLY zxma-sm-mm 15 ms 3,894,476

COMPRESSED AIR SUPPLY SELF-ADJUSTING LOAD BALANCING PNEUMATIC I-IOISTThe present invention relates generally to a pneumatic hoist, and moreparticularly to a load balancing system for such a pneumatic hoistwherein the load supported by the hoist may be vertically displaced byapplying a relatively light force to the load. This invention was madein the course of, or under, a contract with the United States AtomicEnergy Commission.

In the fabrication of relatively heavy and complex equipment such asnuclear reactors or in the loading of heavy workpieces in precisionmetal working machines, there is often a need to follow meticuloushandling procedures to effect the desired assembly without damage. Theweight of many of these components or workpieces necessitates the use oflifting mechanisms for setting them into their desired position.However, due to inaccurate control of lifting mechanisms, the componentsare often damaged during the assembly. Efforts to obviate or minimizestructural damage to components include the use of pneumatic hoistswhich substantially overcome many of the problems attendant with the useof other types of hoists. However, it was found that the commerciallyavailable pneumatic hoists did not accurately respond to the light forcedesired for moving a workpiece small distances and lacked the means ofbeing easily and readily adjusted to the precise weight of each loadhandled. In fact, most of the commercially available pneumatic hoistsrequired that in order to move a load from a fixed position to a newposition, the volume of air in the hoist must be increased or decreasedby manually operating a valve separate from the hoist. With the loadbalanced against the pressure on the piston in a fixed position in orderto move the piston and the load attached thereon, the operator mustoperate suitable valving to overcome the pressure acting upon thepiston. In some of the more advanced pneumatic hoists, the air pressureapplied to the piston is controlled by throttling an orifice or bleedingan aperture, or by manually adjusting a regulator. These previouslyavailable hoists were not found to supply satisfactory solutions forproviding the required ease of handling and resisting the forces ofimpact upon the components or workpieces being assembled.

E Accordingly, it is the primary aim or goal of the present invention toprovide a pneumatic hoist with a control system wherein the liftingforce of the hoist is automatically adjusted to the load and by applyinga relatively small force on the load in the desired direction to movethe load to the desired location without impact. In other words, withthe present invention, a heavy load supported by the hoist may bevertically displaced by a single operator in much the same manner as ifthe load was of a weight easily supported by the operator. To achievethis objective the pneumatic hoist employs a load balancing system inwhich'the hoist is coupled to a pressure regulator through suitablevalving wherein the regulator utilizes a reference pressureautomatically set to that corresponding to the pressure required tofreely support the load in an initial position and is capable ofcontinuously maintaining the pressure in the hoist to this referencepressure when externally applied forces upon the load change thepressure in the hoist. This capability for automatically setting andmaintaining the pressure in the hoist to maintain a continuous balanceof the load is especially useful for significantly reducing forces ofimpact encountered during handling operations and for providing exactalignment of mating parts.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiment about to be described, orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the invention in practice.

In the accompanying drawing, the figure is a schematic diagram of thepneumatic hoist and control system of the present invention.

A preferred embodiment of the invention has been chosen for the purposeof illustration and description.

The preferred embodiment illustrated is not intended to be exhaustive orto limit the invention to the precise form disclosed. It is chosen anddescribed in order to best explain the principles of the invention andtheir application in practical use to thereby enable others skilled inthe art to best utilize the invention in various embodiments andmodifications as are best adapted to the particular use contemplated.

Described generally, the present invention is an improved pneumatichoist of the type using air in a compression chamber formed by a pistonin a cylinder for supporting a loadattached to the piston, wherein theimprovement comprises a pressure regulator containing a referencepressure chamber and a regulator chamber separated from one another by amovable diaphragm-like structure. This structure is interlinked with anatmospheric vent and a compressed air supply for changing the pressurein the regulator chamber in response to movement of the structure untilthe pressure in all three chambers is balanced. Valve means are used forselectively interconnecting the reference pressure chamber and theregulator chamber with the compression chamber in the hoist so as tofirst equalize the loadsupporting pressure in the compression chamberwith the pressure in the reference pressure chamber and thereafterisolate the pressure in the reference chamber and connecting thecompression chamber with the regulator'chamber. Pressure changes in thecompression chamber,- resulting from the application of an externalforce on the load, move the diaphragmmounted piston to either vent airfrom or receive air into the regulator chamber until the pressure in thecompression chamber is equal to the pressure in the reference pressurechamber. This capability of maintaining the proper continuous pressurein the compression chamber provides the desired continuous balancedsupport of the load.-

Described in greater detail and with reference to the accompanyingdrawing, the pneumatic hoist is generally shown at 10 supporting a load12 with the primary lifting support provided by a crane 14 attached tothe hoist. The pneumatic hoist is shown comprising a cylinder 16containing a movable piston 18 therein with a piston rod 20 affixed tothe piston 18 and the load 12 whereby vertical displacement of thepiston 18 moves the load. The support of the load is provided by airpressure acting upon the piston from within a compression chamber 21defined by the piston and cylinder. To assure minimal air leakage fromchamber 21, seals 22 and 24 are provided about the piston rod and thepiston, respectively. A vent 26 is provided through the cylinder wall onthe side of the piston opposite chamber 21 to equalize the pressure inthe upper part of the cylinder with the surrounding ambient pressure asthe volume of the cylinder changes with relocation of the pis-' ton. Ofcourse, if desired, by merely inverting the arrangement shown, thepiston rod may be coupled to the crane and the cylinder may be coupledto the load.

The control system for automatically setting and maintaining the airpressure for supporting the load12 and for maintaining that pressure asthe load 12 moves in response to the application of an externallyapplied force by a human operator or human controlled mechanism is showncomprising a regulator 28 and attendant valves and conduits which willbe discussed below. The regulator 28 comprises a housing 30 containing adiaphragm-like piston 32 therein which divides the housing 30 intochambers 34 and 36. The piston 32 is provided with a passageway 38 whichcommunicates with the chamber 34 and atmosphere. The chambers in housing30 are placed in registry with chamber 21 of the hoist by a conduit 40,a two-way selector valve 42, and conduits 44 and 46 which communicatewith chambers 34 and 36 of housing 30, respectively. The chamber 34 isalso connected to a compressed air supply 48 -through a conduit 50.Chamber 34 contains a valve means 52 which adjusts the pressure thereinby either bleeding air from the chamber through passageway 38 or byallowing pressurized fluid from air source 48 to enter chamber 34through conduit 50. This valve means 52 is shown comprising a ball 54 incontact with the opening of passageway 38 in piston 32 and a ball 56 invalve 57 that is in contact with and seals the opening of conduit 50 inchamber 34. The balls 54 and 56 are interconnected by a rod 58 and arenormally held by bias spring 60 in positions which close passageway 38and conduit 50, as shown, so that both passageways are sealed when thepressures on both sides of piston 32 are equalized or are discreetlyopened as these pressures differ. In order to provide the hoist with themass of pressurized air necessary to initially support the load 12, aconduit 62 is connected between the compressed air supply 48 andcompression chamber 21 in the hoist 10 which contains a valve 64 forcontrolling the flow of air to chamber 21. With piston 18 at its lowposition valve 64 is held in the open position, the compressed airpasses through conduit 62 into chamber 21 until the piston 18 moves inan upward direction to suspend the load 12. When the load is in thedesired vertical position, that is with piston 18 out of contact withvalve 64, the valve 64 is closed to terminate the flow of air intochamber 21. During this flow of air into chamber 21, I

the valve 42 is in a position which blocks communication betweenchambers 34 and 21 and simultaneously places chamber 36 in registry withchamber 21 so as to equalize or balance the pressure of the air inchamber 36 with that in chamber 21. Also, as the air flows into chamber36 via conduits 40 and 46, the piston 32 is displaced or flexeddownwardly to move ball 56 off its seat so as to allow compressed air toflow into chamber 34 until the pressures in chambers 34 and 36 arebalanced. With the load supported by the air pressure against piston 18,the valve 42 is repositioned so as to place cham' ber 34 in registrywith the chamber 21 of the hoist via conduits 40 and 44. This movementof the valve isoas a reference pressure corresponding to the pressure ofair necessary for the hoist to support the load.

ator will slightly move .the piston. 18 upwardly so as to decrease theair'pressure in both chamber 21 of the hoist l0 and chamber 34 ofregulator 28. This decrease air pressure will cause the piston 32 to beflexed downwardly due to the greater pressure of the air in chamber 36.This downward movement of the piston moves ball 56 off its seat so as toplace the chamber 34 incommuni cation with the air supply 48. With thiscommunication established, pressurized air enters chambers 34 and 21until the load change is removed and the pressure in chamber 34 is againbalanced with chamber 36 so as to return piston 32 to its initialposition where ball 56 again seals conduit 50. The admittance of thepressurized fluid to chamber 21 during this vertical movement of theload allows piston 18 and the load to be placed in a new positionindicative of the forces applied by the operator against the load. Alternatively, a downwardly directed force applied by the operator againstthe load 12 causes the air pressure in chambers 21 and 34 to beincreased to a pressure greater than the reference pressure in chamber36 so as to move the piston 32 in an upward direction and therebypulling the piston 32 away from the ball 54 for opening passageway 38 toatmosphere. With this opening established, the air pressure in chambers21 and 34 is decreased until the load change is removed and with thepressures in chambers 34 and 36 again in balance, the piston 32 isreturned toits initial position by the action of the pressure in chamber36. The weight of the supported load may be easily determined bymonitoring the pressure in the chamber 21 by employing a simple airpressure gage calibrated in the desired weight units as shown at 66 inconduit 40.

In the event a predetermined constant force is desired to be applied bythe hoist, the mass of air necessary to provide this force may beadmitted into chamber 21 through a conduit 68 coupling this chamber withthe air supply 48 while valve 42 is maintained in position to connectchambers 21 and 36. A valve 70 in conduit 68 is selectively operable forproviding this load lifting force against the piston 18.

When the load 12 is placed in its desired position and the hoist is nolonger required for supporting the load, the pressure within chamber 21of the hoist is released by the action of regulator 28 when the pressurein chamber 36 is reduced to that of the atmosphere by the operation ofvalve 72 in conduit 74 which is connected to chamber 36 via conduit 46.

It will be seen that the present invention provides a unique controlover the movement and control of relatively heavy loads by continuouslysupporting the load and allowing its position and speed of movement tobe in response to a low effort command of the operator. The only contactforce between the load and its support is the applied force used by theoperator to move the load. The air pressure required for the operationof the subject invention may be about psig with the the load beinglifted. For example, air consumption has been measured at less than 10standard cubic feet per hour (scfh) while holding a lSOO pound load in aballates chamber 36 so as to maintain the pressure therein ancedposition. The ,insta ntaneous demand for a few seconds required toestablish albalanced condition is In operation, with valve 42 placingthe chambers 21 and 34 in registry, application of a force againstthevload 12 in a vertical upward direction by a human'operaboutlZS scfh,Theair requirements for balancing the load and for lifting arloadarehigher than that required for maintaining-the-systern ,in a balancedcondition. The amount of air required is also dependent upon weight ofthe load being lifted. Of course, as described above, no air flow fromthe compressed air supply is employed during load descent. As an exampleof the relatively light forces required of the human operator forvertically displacing a supported load, a load of 760 pounds requires anexternally applied force of only about 0.75 pounds to effect movement.The velocity of travel is roughly proportional to the force applied. Theexternally applied force may be held for a relatively long duration toeffect a substantial vertical displacement of the load or for arelatively short duration to effect a vertical displacement in the orderof a fraction of an inch. The capability of this system for minimizingthe forces of impact has been dramatically demonstrated by manuallysetting the 760-pound weight on a styrofoam cup with the cup actuallylimiting (without rupturing) the downward movement of the load. Thelifting capabilities of the hoist of the subject invention are limitedby the particular size of the hoist and attendant components so as toprovide a system which may be utilized to handle loads of several tonsor as low as a few pounds.

As various changes may be made in the form, construction, andarrangement of the parts herein without departing from the spirit andscope of the invention and without sacrificing any of its advantages, itis to be understood that all matter herein is to be interpreted asillustrative and not in a limiting sense.

What is claimed is:

l. A pneumatic hoist positionable between a load and load liftingmechanism for automatically maintaining the load in a selected verticalposition provided upon displacing the load by exerting an externallyapplied force thereon and for significantly reducing the force requiredto effect the displacement of the load, comprising a cylinder and pistonassembly with said cylinder connectable to one of said load and saidlifting mechanism and said piston connectable to the other of said oneof said load and said lifting mechanism, a housing, movable piston meansdisposed in said housing for dividing the latter into first and secondchambers, a passageway in said piston means communicating with saidfirst chamber and atmosphere, conduit means in registry with both ofsaid chambers and further chamber on one side of said piston in saidcylinder, valve means in said conduit means for selectively placingeither the first or second chamber in communication with said cylinder,a further conduit means in registry with said first chamber forintroducing a flow of pressurized air thereinto from a compressed airsupply, and further valve means in said first chamber for regulating theflow of said air through said passageway to atmosphere and into saidfirst chamber from said further conduit means in response to thedirection of movement of said piston means with said movement beingresponsive to the pressure differential in said first chamber and saidsecond chamber.

2. The pneumatic hoist claimed in claim 1, wherein an additional conduitmeans connects said further chamber and said compressed air supply,additional valve means are in said additional conduit means for placingsaid further chamber in registry with said compressed air supply forintroducing compressed air into said further chamber, and wherein thefirst mentioned valve means places said second chamber in registry withsaid compressed air supply through said additional conduit meanssimultaneously with said further chamber.

3. The pneumatic hoist claimed in claim 2 wherein a still furtherconduit means connects said further chamber and said compressed airsupply, and wherein valve means are disposed in said still furtherconduit means contiguous to said further chamber and contactable by saidpiston for effecting flow of compressed air through said still furtherconduit means into said further chamber.

4. The pneumatic hoist claimed in claim 1 wherein valve means are inregistry with said second chamber for discharging compressed air thereinto atmosphere.

5. The pneumatic hoist claimed in claim 1 wherein said further valvemeans comprises a first ball engageable with the passageway in saidpiston means, a second ball engageable with said further conduit means,a rod interconnecting said balls, and bias means urging both of saidfirst ball and said second ball into an air flow inhibiting engagementwith said passageway and said further conduit means, and wherein saidpiston operates said further valve means to selectively establishcommunication between said first chamber and atmosphere and said firstchamber and said compressed air supply when the pressure in said firstchamber is respectively greater and less than the pressure in saidsecond chamber.

1. A pneumatic hoist positionable between a load and load liftingmechanism for automatically maintaining the load in a selected verticalposition provided upon displacing the load by exerting an externallyapplied force thereon and for significantly reducing the force requiredto effect the displacement of the load, comprising a cylinder and pistonassembly with said cylinder connectable to one of said load and saidlifting mechanism and said piston connectable to the other of said oneof said load and said lifting mechanism, a housing, movable piston meansdisposed in said housing for dividing the latter into first and secondchambers, a passageway in said piston means communicating with saidfirst chamber and atmosphere, conduit means in registry with both ofsaid chambers and further chamber on one side of said piston in saidcylinder, valve means in said conduit means for selectively placingeither the first or second chamber in communication with said cylinder,a further conduit means in registry with said first chamber forintroducing a flow of pressurized air thereinto from a compressed airsupply, and further valve means in said first chamber for regulating theflow of said air through said passageway to atmosphere and into saidfirst chamber from said further conduit means in response to thedirection of movement of said piston means with said movement beingresponsive to the pressure differential in said first chamber and saidsecond chamber.
 2. The pneumatic hoist claimed in claim 1, wherein anadditional conduit means connects said further chamber and saidcompressed air supply, additional valve means are in said additionalconduit means for placing said further chamber in registry with saidcompressed air supply for introducing compressed air into said furtherchamber, and wherein the first mentioned valve means places said secondchamber in registry with said compressed air supply through saidadditional conduit means simultaneously with said further chamber. 3.The pneumatic hoist claimed in claim 2 wherein a still further conduitmeans connects said further chamber and said compressed air supply, andwherein valve means are disposed in said still further conduit meanscontiguous to said further chamber and contactable by said piston foreffecting flow of compressed air through said still further conduitmeans into said further chamber.
 4. The pneumatic hoist claimed in claim1 wherein valve means are in registry with said second chamber fordischarging compressed air therein to atmosphere.
 5. The pneumatic hoistclaimed in claim 1 wherein said further valve means comprises a firstball engageable with the passageway in said piston means, a second ballengageable with said further conduit means, a rod interconnecting saidballs, and bias means urging both of said first ball and said secondball into an air flow inhibiting engagement with said passageway andsaid further conduit means, and wherein said piston operates saidfurther valve means to selectively establish communication between saidfirst chamber and atmosphere and said first chamber and said compressedair supply when the pressure in said first chamber is respectivelygreater and less than the pressure in said second chamber.